Failover Server

About a year ago I built a server (Fedora Core 7) which is acting a primary domain controller for a small network. (About 25 users). Its been working terrific, with little or no issues. I would, however, like to implements a failover system.

The server has all the bling (Hardware RAID-5, with a hotspare, data backups going to a remote systems), but if she smokes I would love to have the ability to SSH into a failover system from home, modify a few configs and have everyone up and running. I guess this would entail immediate replication of all writes to the PDC.

Any thoughts? I know that Samba can be configured to act as a Backup Domain Controller. I am not using LDAP, I am using a PAM backend, which may complicate things.